Methods and apparatuses for promoting fusion of vertebrae

ABSTRACT

Methods and apparatuses for promoting fusion of vertebrae are provided. The apparatuses comprise interconnecting plates that fixate vertebrae to each other and provide for a predetermined amount of subsidence where the fusion occurs. Allowing for this predetermined amount of subsidence increases bone to bone contact at the graft, which promotes fusion without having excessive settling of the two vertebrae onto the graft. The predetermined amount of subsidence is achieved by the placement of a plate spacer between each of two interconnecting plates when the plates are attached to the vertebrae. The plate spacer has a height equal to the maximum amount of subsidence desired. After affixing the plates to the vertebrae, the plate spacer is removed, leaving a space between the plates, which allows the vertebrae to subside by a distance equal to the height of the plate spacer.

Cross-Reference to Related Application

This application claims the benefit of U.S. Provisional Application60/359,875, filed Feb. 25, 2002.

BACKGROUND

(1) Field of the Invention

The present invention relates to methods and apparatuses for stabilizingvertebrae when fusing the vertebrae.

(2) Description of the Related Art

Fusion of vertebrae is often necessary to relieve debilitating pain orcorrect a deformity. When vertebrae are fused, e.g., with bone grafts,graft extenders, or interbody spacers such as interbody cages or boxes(collectively termed “grafts” herein), it is desirable to stabilize thefused vertebrae using an apparatus such as a plate to fixate onecervical vertebra to another to promote fusion across motion segments.

There are various known apparatuses useful for stabilizing vertebraewhen the vertebrae are fused. See, e.g. U.S. Pat. Nos. 4,743,260;5,603,703; 5,458,641; 5,827,328; and 6,080,193.

The known apparatuses are generally useful to prevent horizontaldisplacement of the two grafted vertebrae. They also can preventexcessive compression of the two vertebrae, which can lead to a weakfusion or even collapse of the graft. However, the apparatuses can alsolead to stress shielding, in which fusion of the vertebrae to thegrafted bone is impeded or prevented entirely because the apparatusprevents adequate contact between the vertebra and the graft. Resorptionof the bone graft can exacerbate this problem. It is well known in theart that some subsidence, or settling, between the vertebrae at thegraft is advantageous to quickly forming a strong fusion. The subsidenceincreases bone to bone contact, which is well known to enhance bonefusion, as predicted by Wolff's law, by enhancing physiologicalprocesses involved in bone remodeling (Kowalski et al., 2001, Neurol.Focus 10 (4) Article 2).

The problem of stress shielding is partially addressed in U.S. Pat. No.5,843,082, which provides an apparatus having a plate on each vertebra,and a pair of longitudinal rods which interconnect the plates. Theplates can slide along the rods vertically, which allows for subsidencebetween the vertebrae. There is no suggestion therein that the amount ofsubsidence could or should be controlled using that apparatus. Thus,while the apparatus in the '082 patent does not cause stress shielding,it also does not prevent excessive subsidence.

It is therefore an object of the present invention to provide improvedapparatuses and methods for promoting optimal fusion at a graft,particularly at cervical vertebrae.

It is a further object of the invention to provide improved apparatusesand methods for stabilizing the fusion that minimize stress shielding.

It is an additional object of the invention to provide apparatuses andmethods for minimizing stress shielding as well as excessive subsidenceat vertebral fusions, thus promoting optimal fusion at the graft.

It is a still further object of the invention to provide an apparatusthat accomplishes the above objects yet is compact in size and utilizesa minimum amount of parts.

SUMMARY OF THE INVENTION

It has been found that the above and related objects of the presentinvention are obtained by the use of slidably interconnected plates thatfixate vertebrae to each other and provide for a predetermined amount ofsubsidence at the fusion site. This predetermined subsidence increasesbone to bone contact at the graft, which promotes fusion without havingexcessive compression of the two vertebrae onto the graft. Thepredetermined subsidence is achieved by the placement of a plate spacerbetween each of two interconnecting plates when the plates are attachedto the vertebrae. The plate spacer has a height equal to the amount ofsubsidence desired. After affixing the plates to the vertebrae, theplate spacer is removed, leaving a space between the plates, whichallows the vertebrae to subside by a distance equal to the height of theplate spacer.

Accordingly, in some embodiments, the present invention is directed toapparatuses for promoting fusion of a first vertebra and a secondvertebra in a spinal column at a graft between the first vertebra andthe second vertebra.

A preferred embodiment of these apparatuses comprises a first platemountable to the first vertebra, and a second plate mountable to thesecond vertebra. The first plate comprises integral means for slidablyinterconnecting with the second plate, the sliding occurring parallel tothe long axis of the spinal column. The means for slidablyinterconnecting the first and second plates prevents rotational andtransverse movement of the first vertebra relative to the secondvertebra.

Preferably, the first plate has a first base mountable to the firstvertebra and a tongue protruding from the first base with an end distalto the first base and two sides perpendicular to the end. Also, thesecond plate has a second base with two sides and a top. The second baseis capable of attachment to the second vertebra, and the second platehas a groove formed by the top of the second base and inner edges of thetwo sides of the second base. In these embodiments, the tongue of thefirst plate and the groove of the second plate slidably interconnectwhen attached to the first and second vertebrae, the interconnectionoccurring at the two sides of the tongue of the first plate and theinner edges of the two sides of the groove of the second plate.Additionally, the end of the tongue and the top of the second base arecapable of touching, preventing compression of the first vertebra withthe second vertebra at the graft between the two.

These apparatuses preferably also comprise a removable plate spacersuitable for placing between the first plate and the second plate.

In additional preferred embodiments of the apparatuses, the apparatuscomprises a first member for attachment to the first vertebra and asecond member for attachment to the second vertebra, along with a meansfor attaching the apparatus to the first vertebra at the first member, ameans for attaching the apparatus to the second vertebra at the secondmember, a means for preventing rotational and transverse movement of thefirst vertebra relative to the second vertebra, and a plate spacercomprising a height, where the plate spacer is capable of insertion intothe apparatus between the first member and the second member. In theseembodiments, the plate spacer can be removed from the apparatus afterthe apparatus is attached to both the first vertebra and the secondvertebra, and the height of the plate spacer provides a subsidencebetween the two vertebrae upon removal of the plate spacer, thesubsidence being equivalent to the height of the plate spacer.

In still other preferred embodiments, the invention is directed toapparatuses for promoting fusion of a first vertebra and a secondvertebra in a spinal column at a graft between the first vertebra andthe second vertebra. The apparatuses comprise a first plate mountable tothe first vertebra, a second plate mountable to the second vertebra, anda removable plate spacer suitable for placing between the first plateand the second plate, where the plate spacer comprises a height. Inthese embodiments, the first plate comprises an integral means forslidably interconnecting with the second plate, where the sliding occursparallel to the long axis of the spinal column. This means preventsrotational and transverse movement of the first vertebra relative to thesecond vertebra. The apparatuses of these embodiments further comprise ameans for limiting axial extension of the first plate with respect tothe second plate.

The invention is also directed to apparatuses for promoting fusion of afirst vertebra, a second vertebra and a third vertebra in a spinalcolumn at grafts between (a) the first vertebra and the second vertebraand (b) the second vertebra and the third vertebra. The apparatusescomprise a first plate mountable to the first vertebra, a second platemountable to the second vertebra, and a third plate mountable to thethird vertebra. In these embodiments, the first plate and the thirdplate comprise integral means for slidably interconnecting with thesecond plate, where the sliding occurs parallel to the long axis of thespinal column. This means prevents rotational and transverse movement ofthe first vertebra relative to the second vertebra and the secondvertebra relative to the third vertebra.

In related embodiments, the invention is directed to apparatuses forpromoting fusion of n adjacent vertebrae in a spinal column at graftsbetween each of the n vertebrae. The apparatuses comprise n plates, eachplate mountable to one of each of the n vertebrae. Each plate alsocomprises integral means for slidably interconnecting with adjacentplate(s), where the sliding occurs parallel to the long axis of thespinal column. This means prevents rotational and transverse movement ofeach of the n vertebrae relative to each adjacent vertebra(e) of the nvertebra.

The above apparatuses are useful in methods for promoting fusion of afirst vertebra with a second vertebra in a spinal column. A preferredembodiment of the methods comprises providing an apparatus, theapparatus comprising a means for attaching the apparatus to the firstvertebra at a first member; a means for attaching the apparatus to thesecond vertebra at a second member; a means for preventing rotationalmovement of the first vertebra relative to the second vertebra; and aplate spacer comprising a height. The plate spacer is capable ofinsertion into the apparatus between the first member and the secondmember such that the plate spacer can be removed from the apparatusafter the apparatus is attached to both the first vertebra and thesecond vertebra. In these methods, the apparatus is attached to thefirst vertebra at the first member; the means for preventing rotationaldisplacement of the first vertebra from the second vertebra is partiallyengaged; the plate spacer is placed between the first member and thesecond member; the means for preventing rotational displacement issubstantially fully engaged such that the first member and the secondmember each abut the plate spacer; the apparatus is attached to thesecond vertebra at the second member; and the plate spacer is removedfrom between the first member and the second member.

The invention is also directed to any of the novel plates used in any ofthe above apparatuses and methods, including but not limited to thefollowing: (a) a plate with a base mountable to the vertebra, the platealso having a tongue protruding from the base with an end distal to thebase and two sides perpendicular to the end; (b) a plate with a basemountable to the vertebra, the base having two sides and a top, theplate having a groove formed by a top of the base and inner edges of thetwo sides of the base; (c) a plate with a base mountable to thevertebra, the plate also having a first tongue protruding from the basewith an end distal to the base and two sides perpendicular to the end,the plate also having a second tongue protruding from the base with anend distal to the base and two sides perpendicular to the end, whereinthe first tongue and the second tongue are directed in oppositedirections along the long axis of the spinal column; (d) a plate with abase mountable to the vertebra, the plate also having a tongueprotruding from the base with an end distal to the base and two sidesperpendicular to the end, the plate also having a groove formed by a topof the base and inner edges of the two sides of the base, wherein thetongue and the groove are directed in opposite directions along the longaxis of the spinal column; and (e) a plate with a base mountable to thevertebra, the base having two sides, a top and a bottom, the platehaving a first groove formed by the top of the base and inner edges ofthe two sides of the base, the plate also having a second groove formedby the bottom of the base and inner edges of the two sides of the base,wherein the first groove and the second groove are directed in oppositedirections along the long axis of the spinal column.

BRIEF DESCRIPTION OF THE DRAWING

These and other objects, features and advantages of the presentinvention will be more fully understood by reference to the followingdetailed description of the presently preferred, albeit illustrative,embodiments of the present invention wherein:

FIG. 1 is an elevational view of an apparatus constructed in accordancewith the present invention for stabilizing two vertebrae, as seen beforeremoval of the plate spacer;

FIG. 2 is a cross sectional view of the apparatus of FIG. 1, showing theinterconnection between the two plates at the tongue and groove sectionslocated on line 2-2 in FIG. 1; FIG. 2 a shows an alternate form suitablefor interconnecting the two plates;

FIG. 3 is a view of the apparatus of FIG. 1, taken along the sagittalplane as indicated by line 3-3 in FIG. 1; and

FIG. 4 is a view of one embodiment of the plate spacer of the apparatusof FIG. 1.

FIG. 5 is a view of an alternative embodiment of plate 12 illustrated inFIG. 1-3.

FIG. 6 is a view of an additional alternative embodiment of plate 12illustrated in FIG. 1-3.

FIG. 7 a and 7 b are views of alternative embodiments of plate 14illustrated in FIG. 1-3; FIG. 7 c and 7 d is a view of an additionalalternative embodiments of plate 12 illustrated in FIG. 1-6; FIG. 7 eare views of alternative embodiments of plates 12 and 14 illustrated inFIG. 1-6.

FIG. 8 a, 8 b and 8 c are views of three plates constructed inaccordance with the present invention useful for stabilizing three ormore vertebrae.

FIG. 9 a, 9 b and 9 c are elevational views of three apparatusesconstructed in accordance with the present invention for stabilizingthree vertebrae, as seen before removal of the plate spacers, theapparatuses variously using the plates illustrated in FIG. 5-8.

FIG. 10 a, 10 b, 10 c and 10 d are elevational views of four apparatusesconstructed in accordance with the present invention for stabilizingfour vertebrae, as seen before removal of the plate spacers, theapparatuses variously using the plates illustrated in FIG. 5-8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides methods and apparatuses for stabilizingvertebrae while simultaneously minimizing stress shielding and excessivesubsidence. To achieve this, apparatuses are utilized that have at leasttwo separate members, one member being attached to each of thevertebrae. The members that are adjacent to each other can beinterconnected to prevent rotational and transverse displacement of thetwo vertebrae in relation to each other. Additionally, the apparatusespreferably include plate spacer(s) of a preselected height that isplaced between each two adjacent members when the members are attachedto the vertebrae, such that the members are separated by the height ofthe plate spacer. After attachment of the members to the vertebrae, theplate spacer(s) is/are removed. This allows for subsidence of the eachtwo adjacent vertebrae by a distance equal to the height of the platespacer. Thus, stress shielding as well as excessive subsidence isminimized.

In preferred embodiments, the methods and apparatuses are used forfusion of cervical vertebrae, because the problem of stress shielding isencountered most often in cervical fusions. However, the methods andapparatuses are also capable of use for fusion of thoracic or lumbarvertebrae.

In some embodiments, the vertebrae to which the apparatuses are attachedare preferably adjacent to each other. However, the apparatuses can bedesigned and utilized to span and stabilize three or more vertebrae.

Referring now to the drawing, and in particular to FIGS. 1 through 4thereof, a preferred embodiment of the apparatuses of the invention isillustrated. This apparatus has two plates, one comprising a tongue, andthe other comprising a groove. The tongue and groove interconnect andslide. Each of the plates is secured to a respective vertebra by twoscrews or similar fasteners such as anchors, etc, as are known in theart. Specifically, FIGS. 1-4 illustrate an apparatus 10 for use inretaining bone portions such as cervical vertebrae V1 and V2 of a humanspinal column C to stabilize the vertebrae with respect to each otherrotationally and along the vertical axis A. The apparatus comprises afirst plate 12, attached to V1, and a second plate 14, attached to V2.These plates, and the screws used to attach them to vertebrae aresurgically implantable and are made of a suitable biocompatiblematerial, such as titanium, titanium alloy, or stainless steel.

As best shown in FIG. 1, the first plate 12 has a base 20 and a tongue22 protruding from the base 20. The tongue 22 comprises an end 24 distalto the base 20 and two sides 26, 28 perpendicular to the end 24. Thefirst plate also has two holes 30, 32 which accommodate screws 34, 36,used to attach the first plate to vertebra V1. Although two holes whichaccommodate screws that project perpendicularly is shown in the figures,the apparatus is not limited to such an arrangement. Any appropriatearrangement of screw types, hole types, and hole numbers is contemplatedas being within the scope of the invention. Thus, the first plate cancomprise three or more holes to provide for three or more screws intothe vertebra, and, although the screw holes 30, 32 shown in FIG. 1accommodate screws that project perpendicularly from the plane of thefirst plate 12, they can be designed to accommodate screws that are atan appropriate angle to provide for a secure attachment to the vertebraV1. Additionally, a locking device to secure the screws can optionallybe incorporated into these apparatuses. Appropriate devices are wellknown in the art.

Vertebra V1, to which the first plate 12 is attached, is shown in FIG. 1as superior to vertebra V2 in the spinal column C. However, vertebra V1could also be inferior to vertebra V2 in the spinal column C, in whichcase the first plate 12 is affixed into V2 with the tongue protrudingupward toward V1. In either case, the first plate 12 is aligned andscrewed into the vertebra such that the tongue 22 is protruding towardvertebra V2. Thus, when vertebra V2 is below vertebra V1, the tongue 22is protruding downward. Conversely, when vertebra V1 is below vertebraV2, the tongue 22 is protruding upward.

The second plate 14 has a base 50 and a groove 58. The groove 58 isformed by an edge 60 at the top of the base 50 and inner edges 62, 64 ofsides 66, 68 protruding from the two sides of the base 50. The sides ofthe groove 66, 68 also each have a top 82 and 84, respectively. Thesecond plate 14 also is shown in FIG. 1 as having two holes 74, 76 whichaccommodate screws 78, 80. As with the first plate, the type, number andprojection angle of screws that anchor the second plate to the vertebraare merely shown as illustrative, and can be substituted by knownmethods as appropriate.

The two sides 26, 28 of the first plate and the opposing inner edges 62,64 of the side members 66, 68 of the second plate 14 are preferablydesigned to interconnect to prevent the two plates from rotationallyseparating. This is achieved in the preferred embodiment in FIGS. 1-4 bythe sides of the tongue of the first plate 26, 28 having protuberancessuch that the center of the side 38 is wider than the top and bottom ofthe tongue 40 (FIG. 2). This allows the tongue to interconnect with thegroove of the second plate 58, which has inner edges 62, 64 that formrecesses complementary to the tongue protuberances, such that the centerof the sides of the groove 82 is narrower than the top and bottom 84(FIG. 2). FIG. 2 a shows an alternate form of this embodiment. However,the apparatuses of these embodiments are not limited to the illustratedmeans for preventing rotational separation of the plates; anyappropriate means for interconnecting the tongue and groove to preventrotational separation of the plates can be utilized. For example, thesides of the tongue of the first plate can have recesses thatinterconnect with protuberances on the inner edges of the groove, asillustrated in FIG. 7 c. In additional embodiments, the interconnectionof the tongue of the first plate and the groove of the second plate isachieved by a wedge formed by the sides of the first plate matching anopposing wedge formed by the inner edges of the side members of thesecond plate.

The space between the end of the tongue 24 and the top of the base ofthe groove 50 can accommodate a plate spacer 100 (exemplified in FIG.4). The plate spacer 100 is used to separate the two plates axiallywhile the plates are being affixed to the vertebrae. Optionally, morethan one plate spacer can be placed between the two plates to achieve agreater separation than provided with one plate spacer. After the platesare affixed, the plate spacer is removed. In preferred embodiments, theplate spacer has a holder 102 that facilitates the removal of the platespacer. As illustrated in FIG. 4, the plate spacer is a rectangularblock and the holder is a tab protruding from the plate spacer. However,the plate spacer and the holder can take any appropriate shape.Additionally, the plate spacer can be placed anywhere that allows it totemporarily separate the two plates axially. For example, the platespacer can be placed between the base of the first plate 20 and the topsof the sides of the groove 82, 84. All that is required is that theplate spacer be suitable for temporarily separating the two plateslongitudinally until they are affixed to the vertebrae.

The plate spacer 100 has a height H that corresponds to the distancethat the two plates 12, 14 are separated when the plate spacer is placedbetween them. The subsidence that can take place between the graftedvertebrae after the apparatus is implanted is equivalent to the heightof the plate spacer. This height can be from 1 to 10 mm, preferably from1 to 5 mm. The selection of the plate spacer height, or the number ofplate spacers, for any particular situation is within the skill of theart without using undue experimentation.

In some instances, there may be a concern that the interconnectingplates, when implanted, could extend axially, during anatomicextensions, to such a degree that the plates become disengaged, withdisastrous consequences. In those instances, the plates can comprise ameans for limiting axial extension of the first plate with respect tothe second plate. An example of such a means is illustrated in FIGS.5-7. FIG. 5 illustrates plate 12′, FIG. 6 illustrates plate 12″, andFIG. 7 c illustrates plate 12′″ any of which would substitute for plate12 of FIGS. 1-3. The three plates 12′, 12″ and 12′″ completelycorrespond to plate 12 in each element except for the indentations 120and 122 in the two sides of the tongue of the plate illustrated in FIG.5, the indentations 124 and 126 in the two sides of the tongue of theplate illustrated in FIG. 6, and the setscrews 180′ and 182′ in the twosides of the tongue of the plate illustrated in FIG. 7 c. The plate 12′or 12″ function with the plate 14′ of FIG. 7 a or plate 14″ of FIG. 7 bto provide the means for limiting axial extension of the plates whenthey are interconnected. The plates 14′ of FIG. 7 a and 14″ of FIG. 7 bcompletely correspond to plate 14 illustrated in FIGS. 1-3 in eachelement except for the tabs 140 and 142 of the plate illustrated in FIG.7 a and the setscrews 180 and 182 of the plate illustrated in FIG. 7 b.When the means for limiting axial extension is employed, the plate 14′or 14″ is slidably interconnected along inner edges 62 and 64 with plate12′ or plate 12″ along the edges 26 and 28 of the tongue 22 as with thepreviously described embodiments illustrated in FIGS. 1-3. The tabs 140and 142 (FIG. 7 a) or the setscrews 180 and 182 (FIG. 7 b) protrude intothe space in the tongue edges 26 and 28 created by the indentations 120and 122 (FIG. 5) or 124 and 126 (FIG. 6) to prevent the two plates fromextending axially to such an extent that the plates disengage.

The engagement of the tabs to limit axial extension proceeds as follows.When the plates are slidably interconnected, the tabs 140 and 142 orsetscrews 180 and 182 are situated such that they do not interfere withthe interconnection. After the plates are slidably interconnected, thetabs 140 and 142 or setscrews 180 and 182 are moved into the spacecreated by the indentations 120 and 122 or 124 and 126. With the tabs140 and 142 illustrated in FIG. 7 a, the tabs are moved by bending thetabs into the space, for example with a pliers, hammer, crimping tool,or by any other means. In the embodiments employing tabs (e.g., FIG. 7a), the tabs must be made of a material that can be readily bent, as isknow in the art. However, as envisioned herein, the means for limitingaxial extension is not limited to bendable protrusions as illustrated inFIG. 7 a or setscrews as illustrated in FIG. 7 b, and can take any formknown in the art to serve the purpose of limiting the axial extension ofthe two plates by protruding into the space created by the indentations120 and 122 or 124 and 126. For example, the tabs can also be a separatepiece of material that, after the plates are slidably interconnected, isscrewed into a screwhole that has been predrilled into the side members66, 68. With the setscrews 180 and 182 illustrated in FIG. 7 b, thesetscrews are screwed into the space, e.g., with a screwdriver.

In alternative preferred embodiments, the means for limiting axialextension of the two plates is provided by a bar spanning the width ofthe tongue and overlapping the sides of the groove. The bar can beaffixed either to the tongue or the sides of the groove. One version ofthese embodiments is provided as FIG. 7D and 7E. Tongue plate 12″″ hasan indentation 184 that accommodates bar 186, which is affixed to tongueplate 12″″ by screws 188, 190 passing through screwholes in the bar andtongue. The ends of the bar 192, 194 overlap the sides of the groove inplate 14″″ in indentations 196, 198, which are wide enough toaccommodate axial extension and compression of the tongue and groveplates with respect to each other as previously described.

Although the means for limiting axial extension of the two plates isillustrated in FIGS. 5-7 as comprising indentations in both sides of thetongue matching tabs or setscrews on both sides of the groove, or a barcrossing the tongue and overlapping the sides of the groove, theinvention is not limited to those illustrated embodiments. For example,the means can be provided, for example, by tabs on the sides of thetongue matching indentations in the sides of the groove, or setscrews inthe side of the tongue (FIG. 7 c), where the sides of the tongue 26, 28are concave, as with plate 12′″ . The means for limiting axial extensioncan also be achieved with the tab/indentation or setscrew/indentationcombination on only one side of the interconnection. Furthermore, themeans for limiting axial extension using a bar crossing the tongue andoverlapping the sides of the groove can be achieved by: affixing the barinto an indentation in the sides of the groove and crossing the tonguein an indentation wide enough to accommodate axial extension orcompression, or affixing a bar with protrubances at either end thatextend into an indentation on in the edges of the groove, etc. Theskilled artisan can also envision similar means for limiting axialextension which are encompassed within the present invention.

It should also be understood that the means for limiting axial extensioncan be engaged either by the end user (i.e., the surgeon) or at thepoint of manufacture, such that the entire apparatus is provided to theend user already assembled.

The preferred embodiments described above are not limited to a tongueand groove arrangement as exemplified in FIGS. 1-7. The first plate needonly comprise integral means for slidable interconnecting with thesecond plate, where the sliding occurs parallel to the long axis of thespinal column, and where the integral means prevents rotational andtransverse movement of the first vertebra relative to the secondvertebra. The skilled artisan could readily devise configurations otherthan the tongue and groove arrangement exemplified in FIGS. 1-4. Forexample, the slidable interconnection of the two plates can be achievedwith two tongues and grooves, or a tongue that is thinner than thesecond plate and that slips into a groove-shaped slot in the secondplate.

Before implantation, the apparatus is sterilized by any appropriatemeans to prevent infection.

To implant the apparatus, the two plates 12, 14 are interconnected andattached to vertebrae with the plate spacer 100 in place. The platespacer is then removed. The interconnection of the plates and attachmentto the vertebrae can be achieved by any sequence of steps.

In a preferred embodiment, the first plate 12, the second plate 14, andthe plate spacer(s) 100 are packaged together as a sterile assembly withremovable fasteners that prevent the assembly from separating. Ifutilized, the means to prevent axial extension is also engaged. Theassembly is aligned to the exposed anterior surface of the two graftedvertebrae. The first plate 12 and the second plate 14 are affixed to thevertebrae using screws 30, 32 and 74, 76 or other conventional fasteningmeans, and the plate spacer 100 and fasteners are then removed.

In another preferred embodiment, the first plate 12 is firstinterconnected to the second plate 14, the plate spacer 100 is placedbetween the first plate and the second plate, the first plate-platespacer-second plate assembly is aligned to the exposed anterior surfaceof the two grafted vertebrae, the first plate 12 and the second plate 14are affixed to the vertebrae, and the plate spacer 100 is then removedand the means to limit axial extension is engaged, if utilized.

In an additional preferred embodiment, after a graft is placed betweenthe two cervical vertebrae to be fused, the first plate 12 is positionedover the exposed anterior surface of the spinal column C such that thebase is over vertebra V1, and the tongue of the first plate 22 protrudesin the direction of vertebra V2. The tongue of the first plate canoptionally extend so far as to overlap the graft site and cover part ofV2. Care must be taken to be sure that the second plate 14, wheninterconnected with the first plate 12, will be situated such that theholes 74, 76 are over an area of vertebra V2 suitable for insertingscrews to affix the second plate 14 with vertebra V2.

With the first plate 22 on vertebra V1, a suitable drill guide and drill(not shown) are used to drill fastener openings in vertebra V1 at thesite on the surface of vertebra V1 of holes 30 and 32. The screws 34 and36 are then inserted through holes 30 and 32 to connect the first plate22 with vertebra V1.

The second plate 14 is then interconnected to the first plate 12 bysliding the groove of the second plate 58 onto the tongue of the firstplate 22, leaving a space between the end of the tongue of the firstplate 24 and the top of the base of the second plate 50. The platespacer is then placed in the space between the first and second plateand the groove of the second plate 58 is further slid onto the tongue ofthe first plate 22 until the end of the tongue of the first plate 24 andthe top of the base of the second plate 50 are separated by the heightof the plate spacer. The second plate 14 is then affixed to vertebra V2using screws, as previously described with the first plate and vertebraV1.

The plate spacer 100 is then removed from the space between the firstplate and the second plate, and the means to limit axial extension isengaged, if utilized. Thus, in operation, the first plate 12 isseparated from the second plate 14 by the height of the plate spacer H.The graft is then subjected to subsidence limited to the distancedefined by the height of the plate spacer H. Minimization of stressshielding is therefore achieved without concern for excessivesubsidence, since the height of the plate spacer H limits the amount ofsubsidence on the graft.

In another preferred embodiment, using procedures analogous to thosedescribed above, the second plate 14 is first affixed to vertebra V2,the first plate 12 is then interconnected to the second plate 14, theplate spacer 100 is placed between the first plate 12 and the secondplate 14, the first plate is affixed to vertebra V1, and the platespacer is removed and the means to limit axial extension is engaged, ifutilized.

The apparatuses and methods for utilizing them described above are notlimited to use with any particular graft material. They may be usedwith, e.g., cancellous autografts, allografts or xenografts, or with anyartificial or natural bone substitutes known in the art. The apparatusesand methods can also be used with any type of graft, including bonegrafts and interbody spacers such as cages or boxes.

The apparatuses of the preferred embodiments described above are usefulfor promoting fusion of two vertebrae even without the plate spacer.When implanted with the interconnecting means engaged but with a spacebetween the two plates, the apparatuses minimize stress shielding(albeit without protection from excessive subsidence) using a morecompact design and fewer parts than prior art apparatuses, e.g., asprovided in U.S. Pat. No. 5,843,082. The compact design is partially dueto the utilization of a means for slidably interconnecting the platesthat is integral with the plates. This is opposed to the apparatusprovided in U.S. Pat. No. 5,843,082, where the means for slidablyinterconnecting the plates is provided by holes in the platesinterconnecting with bars that are external and not integral with theplates.

The invention is also directed to apparatuses that can be more generallydescribed than the embodiments described above. In these embodiments,the invention is directed to apparatuses for promoting fusion of a firstvertebra and a second vertebra in a spinal column with a graft betweenthe first vertebra and the second vertebra. The apparatus comprise afirst member for attachment to the first vertebra and a second memberfor attachment to the second vertebra; means for attaching the apparatusto the first vertebra at the first member; means for attaching theapparatus to the second vertebra at the second member; means forpreventing rotational and transverse movement of the first vertebrarelative to the second vertebra; and a plate spacer comprising a height,the plate spacer capable of insertion into the apparatus between thefirst member and the second member, wherein the plate spacer can beremoved from the apparatus after the apparatus is attached to both thefirst vertebra and the second vertebra. As in the previously describedembodiments, the height of the plate spacer provides a subsidencebetween the two vertebrae upon removal of the plate spacer, saidsubsidence being equivalent to the height of the plate spacer.

Also as with the previously described apparatuses, these apparatuses arenot limited to use with any particular vertebrae, although the preferredvertebrae are cervical vertebrae. Additionally, these devices arepreferably attached to adjacent vertebrae, although they could be usedto stabilize three or more vertebrae.

Applying the above generalized apparatus to the apparatus illustrated inFIGS. 1-4, the first member comprises a first plate having a first basecapable of attachment to the first vertebra, the first plate also havinga tongue protruding from the first base with an end distal to the firstbase and two sides perpendicular to the end; and the second membercomprises a second plate having a second base, the second base havingtwo sides and a top, wherein the second base is capable of attachment tothe second vertebra, the second plate having a groove formed by a top ofthe second base and inner edges of side members protruding from the twosides of the second base.

As with previously described apparatuses, these apparatuses are usefulin methods for promoting fusion of vertebrae. These methods compriseproviding an apparatus, the apparatus comprising: means for attachingthe apparatus to the first vertebra at the first member; means forattaching the apparatus to the second vertebra at the second member;means for preventing rotational displacement of the first vertebra fromthe second vertebra; and a plate spacer capable of insertion into theapparatus between the first member and the second member, wherein theplate spacer can be removed from the apparatus after the apparatus isattached to both the first vertebra and the second vertebra. Theapparatus is then attached to the first vertebra at the first member;the means for preventing rotational displacement of the first vertebrafrom the second vertebra is engaged; the plate spacer is placed betweenthe first member and the second member; the first member is aligned tothe second member at the plate spacer; the apparatus is attached to thesecond vertebra at the second member; and, finally, the plate spacer isremoved from between the first member and the second member. As withother methods of the invention, the above order need not be followed inexecuting the method, except for the last step (removal of the platespacer).

Also as with previously described methods, these methods can be usedwith any vertebrae, but cervical vertebrae are preferred; the methodscan also be used to stabilize more than two vertebrae, although twoadjacent vertebrae are preferred.

The invention is also directed to apparatuses for promoting fusion ofmore than two vertebrae, using plates mountable to each vertebrae. Aswith the previously described apparatuses, each plate comprises integralmeans for slidably interconnecting with adjacent plate(s), where thesliding occurs parallel to the long axis of the spinal column, and wherethe integral means prevents rotational and transverse movement of thevertebrae to which the plates are mounted. Also as with the previousembodiments, the vertebrae are preferably cervical vertebrae. The platescan be fastened to the vertebrae by any means known in the art, forexample with screws that pass through holes in the plates and screw intothe vertebrae. The apparatuses of these embodiments also preferablyinclude a removable plate spacer mounted between each two adjacentplates. The plate spacer is removed after the apparatus is implanted, toallow subsidence at the graft to take plate that is equivalent to theheight of the plate spacer. Also as with previously describedembodiments, the apparatus optionally includes a means for limitingaxial extension of each two adjacent plates relative to each other.These apparatuses also should be sterilized before implantation.

In some preferred embodiments, these apparatuses utilize plates wherethe means for slidably interconnecting the plates are interconnectingtongue and groove elements, as with previously described tongue andgroove elements. In these embodiments, the plates mountable to thevertebrae on the ends (i.e., the first and the third vertebrae if threevertebrae are being fused; or the first and the fourth vertebrae if fourvertebrae are being fused, etc.) are identical to the plates previouslydescribed and illustrated in FIGS. 1-7. The plate on either end can beeither the tongue plate (e.g., FIGS. 5 or 6) or the groove plate (e.g.,FIG. 7 a or 7 b). The plate(s) mountable to the vertebra(e) that are noton the ends (i.e., the second vertebra if three vertebrae are beingfused, or the second and third vertebrae if four vertebrae are beingfused, etc.) have a combination of two tongues, a tongue and a groove,or two grooves, as appropriate to have a slidably interconnecting tongueand groove between each two adjacent plates. An example of each of thethree possible internal plates for these embodiments is illustrated inFIG. 8 a (two tongues), FIG. 8 b (a tongue and a groove), and FIG. 8 c(two grooves). The elements of these internal plates are completelyanalogous in materials, construction, and structure to the platespreviously described and illustrated in FIG. 1-7.

Thus, the plate illustrated in FIG. 8 a has a base 150 mountable to avertebra, with a first tongue 22′ protruding from the base 150 with anend 24′ distal to the base 150 and two sides 26′, 28′ perpendicular tothe end 24′. The plate also has a second tongue 22″ protruding from thebase 150 with an end 24″ distal to the base 150 and two sides 26″, 28″perpendicular to the end. The first tongue 22′ and the second tongue 22″are directed in opposite directions along the long axis of the spinalcolumn.

The plate illustrated in FIG. 8 b has a base 160 mountable to avertebra, with a tongue 22′ protruding from the base 160 with an end 24′distal to the base 160 and two sides 26′, 28′ perpendicular to the end24′. The plate also has a groove 58′ formed by an edge 60′ at the top ofthe base 160 and inner edges 62′, 64′ of the two sides 66′, 68′ of thebase. The tongue 22′ and the groove 58′ are directed in oppositedirections along the long axis of the spinal column.

The plate illustrated in FIG. 8 c has a base 170 mountable to avertebra, with two sides 66′, 68′, a top 172 and a bottom 174. The platealso has a first groove 58′ formed by the top 172 of the base 170 andinner edges 62′, 64′ of the two sides 66′, 68′ of the base 170.Additionally, the plate has a second groove 58″ formed by the bottom 174of the base 170 and inner edges 62″, 64″ of the two sides 66″, 68″ ofthe base. The first groove 58′ and the second groove 58″ are directed inopposite directions along the long axis of the spinal column.

When one of the three plates illustrated in FIGS. 8 a-8 c is utilizedwith two of any of the previously described plates (e.g., as illustratedin FIGS. 1-7) on three fused vertebrae, they are implanted onto thevertebrae as illustrated in FIGS. 9 a, 9 b or 9 c. In those figures, thefirst plate and the second plate slidably interconnect when attached tothe first and second vertebrae. The interconnection occurs at (a) thetwo sides 26, 28 or 26′, 28′ of the tongue of one of the first plate orthe second plate and (b) the inner edges 62, 64 or 62′, 64′ of the twosides of the groove on the other of the first plate or the second plate.Also, the second plate and the third plate slidably interconnect whenattached to the second and third vertebrae. The interconnection occursat (a) the two sides 26, 28 or 26′, 28′ or 26″, 28″ of the tongue of oneof either the second plate or the third plate and (b) the inner edges62, 64 or 62′, 64′ or 62″, 64″ of the two sides of the groove on theother of the second plate or the third plate. Combinations of theseplates other than those illustrated in FIGS. 9A, 9B and 9C are possible,for example the same interconnecting combinations as shown in FIG. 9 canbe utilized where the assembly is turned upside down in relation to thevertebrae.

When two of the three plates illustrated in FIG. 8 is utilized with twoof any of the previously described plates (e.g., as illustrated in FIGS.1-7) on four fused vertebrae, they are implanted onto the vertebrae asillustrated in FIGS. 10 a, 10 b, 10 c, or 10 d. In those figures, thefirst plate and the second plate slidably interconnect when attached tothe first and second vertebrae. The interconnection occurs at (a) thetwo sides 26, 28 or 26′, 28′ of the tongue of one of the first plate orthe second plate and (b) the inner edges 62, 64 or 62′, 64′ of the twosides of the groove on the other of the first plate or the second plate.Also, the second plate and the third plate slidably interconnect whenattached to the second and third vertebrae. The interconnection occursat (a) the two sides 26, 28 or 26′, 28′ or 26″, 28″ of the tongue of oneof either the second plate or the third plate and (b) the inner edges62, 64 or 62′, 64′ or 62″, 64″ of the two sides of the groove on theother of the second plate or the third plate. Additionally, the thirdplate and the fourth plate slidably interconnect when attached to thethird and fourth vertebrae. The interconnection occurs at (a) the twosides 26, 28 or 26′, 28′ or 26″, 28″ of the tongue of one of either thethird plate or the fourth plate and (b) the inner edges 62, 64 or 62′,64′ or 62″, 64″ of the two sides of the groove on the other of the thirdplate or the fourth plate. Combinations of these plates other than thoseillustrated in FIGS. 10 a, 10 b, 10 c and 10 d are possible, for examplethe same interconnecting combinations as shown in FIG. 10 can beutilized where the assembly is turned upside down in relation to thevertebrae.

Generalizing this system with n number of adjacent vertebrae having n−1number of fusions between the n vertebrae, these embodiments encompassapparatuses for promoting fusion of n adjacent vertebrae in a spinalcolumn at grafts between each of the n vertebrae. The n vertebraecomprise a first vertebra, an nth vertebra, and n−2 vertebra(e) betweenthe first vertebra and the nth vertebra. The apparatuses comprise nplates, where each plate is mountable to one of each of the n vertebrae.Each plate comprises integral means for slidably interconnecting withadjacent plate(s). The sliding occurs parallel to the long axis of thespinal column. The integral means prevents rotational and transversemovement of the each of the n vertebrae relative to each adjacentvertebra(e) of the n vertebra. Preferably, there are also n−1 removableplate spacers, each plate spacer mounted between each two adjacentinterconnecting plates.

These embodiments encompass the fusion of two, three, four, five or morevertebrae as exemplified using the apparatuses previously described, andillustrated for example in FIGS. 1-10. Where only two vertebrae arefused, n=2. Of course, there are no vertebrae between the first vertebraand the second vertebra (n−2=0).

These embodiments can also be used to fuse nonadjacent vertebraetogether with an interbody graft in place of the intervening vertebra(e)that has been resected by a surgical procedure, generally known asvertebrectomy or corpectomy. In these scenarios, one, two or morevertebrae are removed or resected and replaced by an interbody spacerknown in the art, such as a long graft or cage.

Where these embodiments utilize the plates exemplified in FIGS. 1-10,the plate mountable to the first vertebra and the plate mountable to thenth vertebra is independently selected from the two plates illustratedin FIGS. 1-7. These can be described as (1) a plate with a base 20mountable to the vertebra, the plate also having a tongue 22 protrudingfrom the base 20 with an end 24 distal to the base 20 and two sides 26,28 perpendicular to the end 24; and (2) a plate with a base 50 mountableto the vertebra, the base having two sides 66, 68 and a top, the platehaving a groove 58 formed by a top of the base and inner edges 62, 64 ofthe two sides 66, 68 of the base 50. The plate mountable to each of then−2 vertebra(e) between the first and the nth vertebrae is independentlyselected from the three plates illustrated in FIG. 8. They can bedescribed as (i) a plate with a base 150 mountable to a vertebra, with afirst tongue 22′ protruding from the base 150 with an end 24′ distal tothe base 150 and two sides 26′, 28′ perpendicular to the end 24′, theplate also having a second tongue 22″ protruding from the base 150 withan end 24″ distal to the base 150 and two sides 26″, 28″ perpendicularto the end, wherein the first tongue 22′ and the second tongue 22″ aredirected in opposite directions along the long axis of the spinalcolumn; (ii) a plate with a base 160 mountable to a vertebra, with atongue 22′ protruding from the base 160 with an end 24′distal to thebase 160 and two sides 26′, 28′ perpendicular to the end 24′, the platealso having a groove 58′ formed by an edge 60′ at the top of the base160 and inner edges 62′, 64′ of the two sides 66′, 68′ of the base,wherein the tongue 22′ and the groove 58′ are directed in oppositedirections along the long axis of the spinal column; and (iii) a platewith a base 170 mountable to a vertebra, with two sides 66′, 68′, a top172 and a bottom 174, the plate having a first groove 58′ formed by thetop 172 of the base 170 and inner edges 62′, 64′ of the two sides 66′,68′ of the base 170, the plate also having a second groove 58″ formed bythe bottom 174 of the base 170 and inner edges 62″, 64″ of the two sides66″, 68″ of the base, wherein the first groove 58′ and the second groove58″ are directed in opposite directions along the long axis of thespinal column. Each plate in the apparatus must also slidablyinterconnect with the adjacent plate(s) when attached to the vertebrae.The interconnection in these embodiments occurs at (a) the two sides 26,28 or 26′, 28′ or 26″, 28″ of the tongue of one of the interconnectingplates, and (b) the inner edges 62, 64 or 62′, 64′ or 62″, 64″ of thetwo sides of the groove other of the interconnecting plates.

As with the analogous embodiments with two plates, these apparatuses canoptionally comprise a means for limiting axial extension of two adjacentplates in relation to each other. For example, as illustrated in FIGS. 8a, 8 b and 8 c, at least one of the two sides of each tongue cancomprise an indentation 120 or 122, and at least one of the inner edges62′, 64′ or 62″, 64″ of the two sides of each groove can comprise a tab140 or 142 or a setscrew (like 180 or 182 of FIG. 7 b), where each tab140 or 142 or setscrew of each groove is engagable into the indentationof a tongue such that the engagement of the tab 140 or 142 or setscrewlimits axial extension of the first plate with respect to the secondplate and the second plate with respect to the third plate when theplates slidably interconnect. Alternatively, at least one of the twosides of each tongue can comprise a tab or a setscrew (like 180′ or 182′of FIG. 7 c) and at least one of the inner edges of the two sides ofeach groove can comprise an indentation, where each tab or setscrew ofeach tongue is engagable into the indentation of a groove such that theengagement of the tab or setscrew limits axial extension of the firstplate with respect to the second plate and the second plate with respectto the third plate when the plates slidably interconnect. The means forlimiting axial extension can also be provided in these embodiments byusing a bar crossing the tongue and overlapping the sides of the groove,as previously described.

In related embodiments, the invention is directed to methods forpromoting fusion of more than one adjacent vertebrae in a spinal columnat grafts between each adjacent two vertebrae. The method comprisesmounting any of the apparatuses which include plate spacers, asdescribed for this purpose above, to the vertebrae, then removing theplate spacers.

The present invention also encompasses any of the novel plates used inthe apparatuses and methods described above.

Other embodiments within the scope of the claims herein will be apparentto one skilled in the art from consideration of the specification orpractice of the invention as disclosed herein. It is intended that thespecification be considered exemplary only, with the scope and spirit ofthe invention being indicated by the following claims.

In view of the above, it will be seen that the several advantages of theinvention are achieved and other advantages attained.

As various changes could be made in the above methods and compositionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

All references cited in this specification are hereby incorporated byreference. The discussion of the references herein is intended merely tosummarize the assertions made by the authors and no admission is madethat any reference constitutes prior art. Applicants reserve the rightto challenge the accuracy and pertinence of the cited references.

1-95. (canceled)
 96. A method for promoting fusion of a first vertebrawith a second vertebra in a spinal column, the method comprising,providing an apparatus, the apparatus comprising a first plate mountableto the first vertebra comprising at least two edges parallel to the longaxis of the vertebrae, and a second plate mountable to the secondvertebra comprising at least two edges parallel to the long axis of thevertebrae, wherein the first plate comprises integral means for slidablyinterconnecting with the second plate at said edges of each plate thatare parallel to the long axis of the vertebrae, said sliding occurringparallel to the long axis of the spinal column, said means preventingrotational movement of the first vertebra relative to the secondvertebra, and wherein the plates can overlap only at the integral meansfor slidably interconnecting at said edges of each plate when the platesare slidably interconnected.
 97. The method of claim 96, wherein thefirst and second vertebrae are cervical vertebrae.
 98. The method ofclaim 96, wherein the first vertebra is adjacent to the second vertebrain the spinal column.
 99. The method of claim 96, wherein the firstplate and the second plate each further comprise holes passing throughthe plate, and fastening means capable of passing through the holes forattaching the plate to the vertebra.
 100. The method of claim 96,wherein the apparatus further comprises a removable plate spacer mountedbetween the first plate and the second plate, said plate spacercomprising a height.
 101. The method of claim 100, wherein the platespacer further comprises a holder and the height of the plate spacer isbetween about 1 mm and 5 mm.
 102. The method of claim 96, wherein theapparatus further comprises means for limiting axial extension of thefirst plate with respect to the second plate.
 103. The method of claim96, wherein the first plate has a first base mountable to the firstvertebra, the first plate also having a tongue protruding from the firstbase with an end distal to the first base and two sides perpendicular tothe end, and the second plate has a second base, the second base havingtwo sides and a top, wherein the second base is capable of attachment tothe second vertebra, the second plate having a groove formed by a top ofthe second base and inner edges of the two sides of the second base,wherein the tongue of the first plate and the groove of the second plateslidably interconnect when attached to the first and second vertebrae,the interconnection occurring at the two sides of the tongue of thefirst plate and the inner edges of the two sides of the second plate,and wherein the end of the tongue and the top of the second base arecapable of touching, preventing compression of the first vertebra withthe second vertebra.
 104. The method of claim 103, wherein the apparatusfurther comprises a removable plate spacer suitable for placing betweenthe first plate and the second plate, said plate spacer comprising aheight, wherein the plate spacer fits between the end of the tongue andthe top of the second base.
 105. The method of claim 103, wherein theapparatus further comprises means for limiting axial extension of thefirst plate with respect to the second plate.
 106. The method of claim105, wherein the means for limiting axial extension is provided with atleast one of the two sides of the tongue of the first plate comprisingan indentation and at least one of the inner edges of the two sides ofthe second base comprising a tab or a setscrew, the tab or setscrewengagable into the indentation when the tongue of the first plate andthe groove of the second plate slidably interconnect.
 107. A method forpromoting fusion of a first vertebra with a second vertebra in a spinalcolumn, the method comprising providing an apparatus, the apparatuscomprising means for attaching the apparatus to the first vertebra at afirst member; means for attaching the apparatus to the second vertebraat a second member; means for preventing rotational movement of thefirst vertebra relative to the second vertebra; and a plate spacercomprising a height, the plate spacer capable of insertion into theapparatus between the first member and the second member, wherein theplate spacer can be removed from the apparatus after the apparatus isattached to both the first vertebra and the second vertebra; attachingthe apparatus to the first vertebra at the first member; partiallyengaging the means for preventing rotational displacement of the firstvertebra from the second vertebra; placing the plate spacer between thefirst member and the second member; substantially fully engaging themeans for preventing rotational displacement such that the first memberand the second member each abut the plate spacer; attaching theapparatus to the second vertebra at the second member; and removing theplate spacer from between the first member and the second member. 108.The method of claim 107, wherein the means for preventing rotationaldisplacement is engaged, the plate spacer is placed between the firstmember and the second member, and the means for preventing rotationaldisplacement is substantially fully engaged before the apparatus isattached to the first vertebra and the second vertebra.
 109. The methodof claim 108, wherein the apparatus further comprises means for limitingaxial extension of the first plate with respect to the second plate.110. The method of claim 107, wherein the apparatus comprises a firstplate mountable to the first vertebra comprising at least two edgesparallel to the long axis of the vertebrae, and a second plate mountableto the second vertebra comprising at least two edges parallel to thelong axis of the vertebrae, wherein the first plate comprises integralmeans for slidably interconnecting with the second plate at said edgesof each plate that are parallel to the long axis of the vertebrae, saidsliding occurring parallel to the long axis of the spinal column, saidmeans preventing rotational movement of the first vertebra relative tothe second vertebra, and wherein the plates can overlap only at theintegral means for slidably interconnecting at said edges of each platewhen the plates are slidably interconnected.
 111. A method for promotingfusion of a first vertebra, a second vertebra and a third vertebra in aspinal column at grafts between (a) the first vertebra and the secondvertebra and (b) the second vertebra and the third vertebra, the methodcomprising providing an apparatus, the apparatus comprising a firstplate mountable to the first vertebra comprising at least two edgesparallel to the long axis of the vertebrae, a second plate mountable tothe second vertebra comprising at least two edges parallel to the longaxis of the vertebrae, and a third plate mountable to the third vertebracomprising at least two edges parallel to the long axis of thevertebrae, wherein the first plate comprises integral means for slidablyinterconnecting with the second plate at said edges of each plate thatare parallel to the long axis of the vertebrae, said sliding occurringparallel to the long axis of the spinal column, said means preventingrotational movement of the first vertebra relative to the secondvertebra, wherein the second plate comprises integral means for slidablyinterconnecting with the first plate and the third plate at said edgesof each plate that are parallel to the long axis of the vertebrae, saidsliding occurring parallel to the long axis of the spinal column, saidmeans preventing rotational movement of the first vertebra relative tothe second vertebra and the second vertebra relative to the thirdvertebra, wherein the third plate comprises integral means for slidablyinterconnecting with the second plate at said edges of each plate thatare parallel to the long axis of the vertebrae, said sliding occurringparallel to the long axis of the spinal column, said means preventingrotational movement of the second vertebra relative to the thirdvertebra, and wherein the plates can overlap only at the integral meansfor slidably interconnecting at said edges of each plate when the platesare slidably interconnected, mounting the first plate to the firstvertebra, the second plate to the second vertebra, and the third plateto the third vertebra, and engaging the means for slidablyinterconnecting the first plate with the second plate and the secondplate with the third plate.
 112. The method of claim 111, wherein theapparatus further comprises a first plate spacer comprising a height,wherein the first plate spacer is inserted between the first plate andthe second plate when the first plate and the second plate are mounted,then removed after the first plate and the second plate are mounted, anda second plate spacer comprising a height, wherein the second platespacer is inserted between the second plate and the third plate when thesecond plate and the third plate are mounted, then removed after thesecond plate and the third plate are mounted.
 113. The method of claim111, wherein the apparatus further comprises means for limiting axialextension of the first plate with respect to the second plate and thesecond plate with respect to the third plate.
 114. A method forpromoting fusion of n adjacent vertebrae in a spinal column at graftsbetween each of the n vertebrae, the method comprising providing anapparatus, the apparatus comprising n plates, each plate mountable to adifferent vertebra, each plate comprising at least two edges parallel tothe long axis of the vertebrae, wherein each plate comprises integralmeans for slidably interconnecting with the adjacent plate at said edgesof each plate that are parallel to the long axis of the vertebrae, saidsliding occurring parallel to the long axis of the spinal column, andwherein the plates can overlap only at the integral means for slidablyinterconnecting at said edges of each plate when the plates are slidablyinterconnected, mounting each plate to that plate's respective vertebra,and engaging each of the means for slidably interconnecting the with theadjacent plate.
 115. The method of claim 114, wherein the apparatusfurther comprises n−1 plate spacers comprising a height, wherein eachplate spacer is inserted between two adjacent plates, where one and onlyone plate spacer is inserted between each two adjacent plates, andwherein each plate spacer is removed after that plate spacer's twoadjacent plates are mounted.
 116. The method of claim 114, wherein theapparatus further comprises a means for limiting axial extension of eachplate with respect to its adjacent plate.